The term "proteins" includes a number of physiologically active and chemically active materials, including enzymes, cofactors, and cofactor analogs.
Many of these materials, but particularly the enzymes, exhibit the capability of promoting many different types of reactions, such as stereospecific reductions, oxidations, isomerizations, specific degradations, complex syntheses, and the like. Unlike most conventional inorganic catalysts, the protein-type substances generally are relatively water-soluble and may be relatively unstable, frequently being usable only once in aqueous solution as a free-component. Economical use of such may depend upon availability of means for recovery, recycling, and regeneration of relatively costly proteinaceous components.
Thus, it can be advantageous to immobilize the protein substance, which then permits multiple or repetitive use of a single quantity of enzyme or other protein, and provides the ability to stop a reaction rapidly by removing the active protein from the reaction solution or vice-versa. In many cases, an enzyme is stabilized in the immobilized form has a much longer active life. The solution containing the components being processed is not contaminated with the protein, thus decreasing separation requirements. For analytical purposes in particular, these protein substances, particularly enzymes, exhibit long half-life, thus reducing reagent preparations.
A variety of immobilization techniques have been proposed in recent years, such as crosslinking without benefit of carrier, crosslinking within carriers or on the surfaces of carriers, covalent attachment to carriers, adsorption on or in carriers, and encapsulation or entrapment.
U.S. Pat. No. 3,912,593 has taught, as one method, the mixing of a nitrogen-containing substance with a hydrous oxide or hydrous hydroxide of a metal such as tin, iron, vanadium, titanium, or zirconium, in an aqueous medium to form a solid metal chelate of the nitrogen-containing substance, and including the formation thereof in situ. However, I have found that the particular hydrous materials taught therein are not necessarily satisfactory. Improvement in reliability clearly has been needed.